1982 Volume 28 Issue 2 Pages 106-110
Bonding between iron ions and soybean protein (produced by the hydrolysis of soybean meal) in an iron-protein compound, which was prepared by mixing the soybean protein and iron (II) sulfate solution, was studied by infrared spectroscopy and an X-ray powder diffraction method. The oxidation state of the predominant iron ions within the compound was +3, but some Fe (II) ions were also present. In the infrared spectrum of the iron-protein compound, the band ascribable to stretching of the COO-group was shifted to the higher frequency side by 40 cm-1 in comparison with that of the free protein. No evidence was found for the formation of any crystalline iron compounds such as Fe2O3, Fe3O4 and FeO in the X-ray powder patterns. The possibility of the formation of gel-like compounds of iron (II) and iron (III) such as Fe(OH)2 and Fe(OH)3, respectively, was excluded, because the hydrolyzed product of iron (II) is easily oxidized to iron (III) and Fe(OH)3 transforms, at least partly to Fe2O3 or Fe3O4 after aging or storing the product in air. Thus, we concluded that the iron ion is bound to the soybean protein molecule through one or more carboxyl groups. Although other coordination sites within the protein molecule could also combine with the iron ions, we could not find evidence for other bondings.
